1. Field of the Invention
The present invention relates to a dielectric-laminate type band-pass filter for use in a portable radio and the like at a the frequency of several hundred MHz to several GHz.
2. Description of the Prior Art
Conventional resonators may be divided roughly into the resonator using a strip line and the resonator using a coil pattern. When producing a band-pass filter by using such resonators, the band-pass filter is so constructed that plural resonators are connected magnetically.
Here, as the resonator using the strip line, there is a resonator of 1/2 wavelength whose line is open at both ends as shown in FIG. 23, and a resonator of 1/4 wavelength whose line is open at one end and short-circuited at the other end as shown in FIG. 24.
Meanwhile, as the resonator using the coil pattern, as shown in FIG. 25, there is the one in which a spiral-shaped coil pattern 201 and an earth pattern 203 are formed on both sides of a dielectric layer 202 which is clamped therebetween.
In the band-pass filter using the above-mentioned conventional resonators, however, such problems as shown hereinafter were encountered respectively.